Conventionally a motor and a power generator are mechanically coupled when electric power is generated by rotating the motor. Originally the motor and the power generator have the same structure, those are called the motor when a rotating body is rotated to obtain a driving force by supplying the electric power, and those are called the power generator when the rotating body is rotated by the driving force to generate an electromotive force in a winding. Therefore, a trial in which the power generation is performed by the rotation of the rotating body while the motor function is exerted by rotating the rotating body, that is, the trial in which the motor function and the power generator function are simultaneously exerted using the same rotating body has been made. As a result of the trial, for example, Patent Document 1 discloses a magnetic rotation motor power generator.
In the magnetic rotation motor power generator of Patent Document 1, the motor function and the power generator function are exerted by an electromagnet and the rotating body in which a permanent magnet is provided. More specifically, a rotating mode is realized when the permanent magnet of the rotating body comes close to the electromagnet, the rotating body is rotated by action and reaction of a magnetic force between the permanent magnet and the electromagnet, a power generation mode is realized until the permanent magnet comes close to the adjacent electromagnet since the permanent magnet passes by the electromagnet, and the permanent magnet changes a magnetic field around a winding of the electromagnet, whereby an electromotive force is generated by electromagnetic induction.    Patent Document 1: Japanese Unexamined Patent Publication No. 2005-245079
However, in the magnetic rotation motor power generator of Patent Document 1, the one electromagnet switches between the rotating mode and the power generation mode to realize the motor function and the power generator function in a time-division fashion. Accordingly, in the magnetic rotation motor power generator, unfortunately the electromotive force cannot continuously be obtained.
In view of the foregoing, an object of the present invention is to provide a unidirectionally-energized brushless DC motor including an AC voltage output winding, the brushless DC motor being able to exert the power generation function of being able to obtain the continuous electromotive force using the same rotating body, and a motor system including the brushless DC motor.